Internet Engineering Task Force (IETF) T. Bray, Ed.
Request for Comments: 7159 Google, Inc.
Obsoletes: 4627, 7158 March 2014
Category: Standards Track
ISSN: 2070-1721
The JavaScript Object Notation (JSON) Data Interchange Format
Abstract
JavaScript Object Notation (JSON) is a lightweight, text-based,
language-independent data interchange format. It was derived from
the ECMAScript Programming Language Standard. JSON defines a small
set of formatting rules for the portable representation of structured
data.
This document removes inconsistencies with other specifications of
JSON, repairs specification errors, and offers experience-based
interoperability guidance.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7159.
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RFC 7159 JSON March 2014
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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material may not have granted the IETF Trust the right to allow
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Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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RFC 7159 JSON March 2014
Table of Contents
1. Introduction ....................................................31.1. Conventions Used in This Document ..........................41.2. Specifications of JSON .....................................41.3. Introduction to This Revision ..............................42. JSON Grammar ....................................................43. Values ..........................................................54. Objects .........................................................65. Arrays ..........................................................66. Numbers .........................................................67. Strings .........................................................88. String and Character Issues .....................................98.1. Character Encoding .........................................98.2. Unicode Characters .........................................98.3. String Comparison ..........................................99. Parsers ........................................................1010. Generators ....................................................1011. IANA Considerations ...........................................1012. Security Considerations .......................................1113. Examples ......................................................1214. Contributors ..................................................1315. References ....................................................1315.1. Normative References .....................................1315.2. Informative References ...................................13Appendix A. Changes from RFC 4627 .................................151. Introduction
JavaScript Object Notation (JSON) is a text format for the
serialization of structured data. It is derived from the object
literals of JavaScript, as defined in the ECMAScript Programming
Language Standard, Third Edition [ECMA-262].
JSON can represent four primitive types (strings, numbers, booleans,
and null) and two structured types (objects and arrays).
A string is a sequence of zero or more Unicode characters [UNICODE].
Note that this citation references the latest version of Unicode
rather than a specific release. It is not expected that future
changes in the UNICODE specification will impact the syntax of JSON.
An object is an unordered collection of zero or more name/value
pairs, where a name is a string and a value is a string, number,
boolean, null, object, or array.
An array is an ordered sequence of zero or more values.
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RFC 7159 JSON March 2014
The terms "object" and "array" come from the conventions of
JavaScript.
JSON's design goals were for it to be minimal, portable, textual, and
a subset of JavaScript.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The grammatical rules in this document are to be interpreted as
described in [RFC5234].
1.2. Specifications of JSON
This document updates [RFC4627], which describes JSON and registers
the media type "application/json".
A description of JSON in ECMAScript terms appears in Version 5.1 of
the ECMAScript specification [ECMA-262], Section 15.12. JSON is also
described in [ECMA-404].
All of the specifications of JSON syntax agree on the syntactic
elements of the language.
1.3. Introduction to This Revision
In the years since the publication of RFC 4627, JSON has found very
wide use. This experience has revealed certain patterns, which,
while allowed by its specifications, have caused interoperability
problems.
Also, a small number of errata have been reported (see RFC Errata IDs
607 [Err607] and 3607 [Err3607]).
This document's goal is to apply the errata, remove inconsistencies
with other specifications of JSON, and highlight practices that can
lead to interoperability problems.
2. JSON Grammar
A JSON text is a sequence of tokens. The set of tokens includes six
structural characters, strings, numbers, and three literal names.
A JSON text is a serialized value. Note that certain previous
specifications of JSON constrained a JSON text to be an object or an
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RFC 7159 JSON March 20144. Objects
An object structure is represented as a pair of curly brackets
surrounding zero or more name/value pairs (or members). A name is a
string. A single colon comes after each name, separating the name
from the value. A single comma separates a value from a following
name. The names within an object SHOULD be unique.
object = begin-object [ member *( value-separator member ) ]
end-object
member = string name-separator value
An object whose names are all unique is interoperable in the sense
that all software implementations receiving that object will agree on
the name-value mappings. When the names within an object are not
unique, the behavior of software that receives such an object is
unpredictable. Many implementations report the last name/value pair
only. Other implementations report an error or fail to parse the
object, and some implementations report all of the name/value pairs,
including duplicates.
JSON parsing libraries have been observed to differ as to whether or
not they make the ordering of object members visible to calling
software. Implementations whose behavior does not depend on member
ordering will be interoperable in the sense that they will not be
affected by these differences.
5. Arrays
An array structure is represented as square brackets surrounding zero
or more values (or elements). Elements are separated by commas.
array = begin-array [ value *( value-separator value ) ] end-array
There is no requirement that the values in an array be of the same
type.
6. Numbers
The representation of numbers is similar to that used in most
programming languages. A number is represented in base 10 using
decimal digits. It contains an integer component that may be
prefixed with an optional minus sign, which may be followed by a
fraction part and/or an exponent part. Leading zeros are not
allowed.
A fraction part is a decimal point followed by one or more digits.
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RFC 7159 JSON March 2014
An exponent part begins with the letter E in upper or lower case,
which may be followed by a plus or minus sign. The E and optional
sign are followed by one or more digits.
Numeric values that cannot be represented in the grammar below (such
as Infinity and NaN) are not permitted.
number = [ minus ] int [ frac ] [ exp ]
decimal-point = %x2E ; .
digit1-9 = %x31-39 ; 1-9
e = %x65 / %x45 ; e E
exp = e [ minus / plus ] 1*DIGIT
frac = decimal-point 1*DIGIT
int = zero / ( digit1-9 *DIGIT )
minus = %x2D ; -
plus = %x2B ; +
zero = %x30 ; 0
This specification allows implementations to set limits on the range
and precision of numbers accepted. Since software that implements
IEEE 754-2008 binary64 (double precision) numbers [IEEE754] is
generally available and widely used, good interoperability can be
achieved by implementations that expect no more precision or range
than these provide, in the sense that implementations will
approximate JSON numbers within the expected precision. A JSON
number such as 1E400 or 3.141592653589793238462643383279 may indicate
potential interoperability problems, since it suggests that the
software that created it expects receiving software to have greater
capabilities for numeric magnitude and precision than is widely
available.
Note that when such software is used, numbers that are integers and
are in the range [-(2**53)+1, (2**53)-1] are interoperable in the
sense that implementations will agree exactly on their numeric
values.
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RFC 7159 JSON March 20147. Strings
The representation of strings is similar to conventions used in the C
family of programming languages. A string begins and ends with
quotation marks. All Unicode characters may be placed within the
quotation marks, except for the characters that must be escaped:
quotation mark, reverse solidus, and the control characters (U+0000
through U+001F).
Any character may be escaped. If the character is in the Basic
Multilingual Plane (U+0000 through U+FFFF), then it may be
represented as a six-character sequence: a reverse solidus, followed
by the lowercase letter u, followed by four hexadecimal digits that
encode the character's code point. The hexadecimal letters A though
F can be upper or lower case. So, for example, a string containing
only a single reverse solidus character may be represented as
"\u005C".
Alternatively, there are two-character sequence escape
representations of some popular characters. So, for example, a
string containing only a single reverse solidus character may be
represented more compactly as "\\".
To escape an extended character that is not in the Basic Multilingual
Plane, the character is represented as a 12-character sequence,
encoding the UTF-16 surrogate pair. So, for example, a string
containing only the G clef character (U+1D11E) may be represented as
"\uD834\uDD1E".
string = quotation-mark *char quotation-mark
char = unescaped /
escape (
%x22 / ; " quotation mark U+0022
%x5C / ; \ reverse solidus U+005C
%x2F / ; / solidus U+002F
%x62 / ; b backspace U+0008
%x66 / ; f form feed U+000C
%x6E / ; n line feed U+000A
%x72 / ; r carriage return U+000D
%x74 / ; t tab U+0009
%x75 4HEXDIG ) ; uXXXX U+XXXX
escape = %x5C ; \
quotation-mark = %x22 ; "
unescaped = %x20-21 / %x23-5B / %x5D-10FFFF
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RFC 7159 JSON March 20148. String and Character Issues8.1. Character Encoding
JSON text SHALL be encoded in UTF-8, UTF-16, or UTF-32. The default
encoding is UTF-8, and JSON texts that are encoded in UTF-8 are
interoperable in the sense that they will be read successfully by the
maximum number of implementations; there are many implementations
that cannot successfully read texts in other encodings (such as
UTF-16 and UTF-32).
Implementations MUST NOT add a byte order mark to the beginning of a
JSON text. In the interests of interoperability, implementations
that parse JSON texts MAY ignore the presence of a byte order mark
rather than treating it as an error.
8.2. Unicode Characters
When all the strings represented in a JSON text are composed entirely
of Unicode characters [UNICODE] (however escaped), then that JSON
text is interoperable in the sense that all software implementations
that parse it will agree on the contents of names and of string
values in objects and arrays.
However, the ABNF in this specification allows member names and
string values to contain bit sequences that cannot encode Unicode
characters; for example, "\uDEAD" (a single unpaired UTF-16
surrogate). Instances of this have been observed, for example, when
a library truncates a UTF-16 string without checking whether the
truncation split a surrogate pair. The behavior of software that
receives JSON texts containing such values is unpredictable; for
example, implementations might return different values for the length
of a string value or even suffer fatal runtime exceptions.
8.3. String Comparison
Software implementations are typically required to test names of
object members for equality. Implementations that transform the
textual representation into sequences of Unicode code units and then
perform the comparison numerically, code unit by code unit, are
interoperable in the sense that implementations will agree in all
cases on equality or inequality of two strings. For example,
implementations that compare strings with escaped characters
unconverted may incorrectly find that "a\\b" and "a\u005Cb" are not
equal.
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RFC 7159 JSON March 20149. Parsers
A JSON parser transforms a JSON text into another representation. A
JSON parser MUST accept all texts that conform to the JSON grammar.
A JSON parser MAY accept non-JSON forms or extensions.
An implementation may set limits on the size of texts that it
accepts. An implementation may set limits on the maximum depth of
nesting. An implementation may set limits on the range and precision
of numbers. An implementation may set limits on the length and
character contents of strings.
10. Generators
A JSON generator produces JSON text. The resulting text MUST
strictly conform to the JSON grammar.
11. IANA Considerations
The MIME media type for JSON text is application/json.
Type name: application
Subtype name: json
Required parameters: n/a
Optional parameters: n/a
Encoding considerations: binary
Security considerations: See [RFC7159], Section 12.
Interoperability considerations: Described in [RFC7159]
Published specification: [RFC7159]
Applications that use this media type:
JSON has been used to exchange data between applications written
in all of these programming languages: ActionScript, C, C#,
Clojure, ColdFusion, Common Lisp, E, Erlang, Go, Java, JavaScript,
Lua, Objective CAML, Perl, PHP, Python, Rebol, Ruby, Scala, and
Scheme.
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RFC 7159 JSON March 2014
Additional information:
Magic number(s): n/a
File extension(s): .json
Macintosh file type code(s): TEXT
Person & email address to contact for further information:
IESG
<iesg@ietf.org>
Intended usage: COMMON
Restrictions on usage: none
Author:
Douglas Crockford
<douglas@crockford.com>
Change controller:
IESG
<iesg@ietf.org>
Note: No "charset" parameter is defined for this registration.
Adding one really has no effect on compliant recipients.
12. Security Considerations
Generally, there are security issues with scripting languages. JSON
is a subset of JavaScript but excludes assignment and invocation.
Since JSON's syntax is borrowed from JavaScript, it is possible to
use that language's "eval()" function to parse JSON texts. This
generally constitutes an unacceptable security risk, since the text
could contain executable code along with data declarations. The same
consideration applies to the use of eval()-like functions in any
other programming language in which JSON texts conform to that
language's syntax.
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RFC 7159 JSON March 2014Appendix A. Changes from RFC 4627
This section lists changes between this document and the text in RFC4627.
o Changed the title and abstract of the document.
o Changed the reference to [UNICODE] to be not version specific.
o Added a "Specifications of JSON" section.
o Added an "Introduction to This Revision" section.
o Changed the definition of "JSON text" so that it can be any JSON
value, removing the constraint that it be an object or array.
o Added language about duplicate object member names, member
ordering, and interoperability.
o Clarified the absence of a requirement that values in an array be
of the same JSON type.
o Applied erratum #607 from RFC 4627 to correctly align the artwork
for the definition of "object".
o Changed "as sequences of digits" to "in the grammar below" in the
"Numbers" section, and made base-10-ness explicit.
o Added language about number interoperability as a function of
IEEE754, and added an IEEE754 reference.
o Added language about interoperability and Unicode characters and
about string comparisons. To do this, turned the old "Encoding"
section into a "String and Character Issues" section, with three
subsections: "Character Encoding", "Unicode Characters", and
"String Comparison".
o Changed guidance in the "Parsers" section to point out that
implementations may set limits on the range "and precision" of
numbers.
o Updated and tidied the "IANA Considerations" section.
o Made a real "Security Considerations" section and lifted the text
out of the previous "IANA Considerations" section.
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RFC 7159 JSON March 2014
o Applied erratum #3607 from RFC 4627 by removing the security
consideration that begins "A JSON text can be safely passed" and
the JavaScript code that went with that consideration.
o Added a note to the "Security Considerations" section pointing out
the risks of using the "eval()" function in JavaScript or any
other language in which JSON texts conform to that language's
syntax.
o Added a note to the "IANA Considerations" clarifying the absence
of a "charset" parameter for the application/json media type.
o Changed "100" to 100 and added a boolean field, both in the first
example.
o Added examples of JSON texts with simple values, neither objects
nor arrays.
o Added a "Contributors" section crediting Douglas Crockford.
o Added a reference to RFC 4627.
o Moved the ECMAScript reference from Normative to Informative and
updated it to reference ECMAScript 5.1, and added a reference to
ECMA 404.
Author's Address
Tim Bray (editor)
Google, Inc.
EMail: tbray@textuality.com
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